Class QueryWrapperFilter

Constrains search results to only match those which also match a provided
query.

This could be used, for example, with a TermRangeQuery on a suitably
formatted date field to implement date filtering. One could re-use a single
QueryFilter that matches, e.g., only documents modified within the last
week. The QueryFilter and TermRangeQuery would only need to be reconstructed
once per day.

reader - a IndexReader instance opened on the index currently
searched on. Note, it is likely that the provided reader does not
represent the whole underlying index i.e. if the index has more than
one segment the given reader only represents a single segment.

Returns:

a DocIdSet that provides the documents which should be permitted or
prohibited in search results. NOTE: null can be returned if
no documents will be accepted by this Filter.